WEDNESDAY, April 29 (HealthDay News) -- The swine-origin influenza A virus H1N1 is susceptible to both neuraminidase inhibitors oseltamivir and zanamivir, but is resistant to the M2 ion channel blockers amantadine and rimantadine, according to a dispatch on April 28 from the U.S. Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report.
Larisa Gubareva, M.D., Ph.D., and colleagues at the CDC's National Center for Infectious and Respiratory Diseases in Atlanta, report that samples from 13 (20 percent) of the 64 patients infected with the virus in the United States as of April 28 were tested for antiviral medication resistance.
Cross-resistance to the adamantane class of anti-influenza drugs was confirmed in all 13 samples due to the presence of the S31N mutation in the virus' M2 protein, but all 13 samples were found to be susceptible to oseltamivir and zanamivir, as well as peramivir and A-315675, new neuraminidase inhibitors currently undergoing clinical trials, the researchers note.
"Compared with M2 blockers, neuraminidase inhibitors previously exhibited lower frequency of antiviral resistance during therapeutic use. However, during the 2007-2008 influenza season, emergence and transmission of oseltamivir-resistant A (H1N1) viruses
was simultaneously detected in several countries in the Northern Hemisphere," notes a related editorial. "As a result, the World Health Organization Global Influenza Surveillance Network and CDC have emphasized the urgent need for close monitoring of resistance to neuraminidase inhibitors."